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Cisco ASR 5000 Session Control Manager

Administration Guide

Version 14.0

Last Updated August 30, 2013

Americas Headquarters

Cisco Systems, Inc.170 West Tasman DriveSan Jose, CA 95134-1706USAhttp://www.cisco.comTel: 408 526-4000

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Text Part Number: OL-27224-07
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THE SPECIFICATIONS AND INFORMATION REGARDING THE PRODUCTS IN THIS MANUAL ARE SUBJECT TO CHANGE WITHOUT NOTICE. ALLSTATEMENTS, INFORMATION, AND RECOMMENDATIONS IN THIS MANUAL ARE BELIEVED TO BE ACCURATE BUT ARE PRESENTED WITHOUT WARRANTYOF ANY KIND, EXPRESS OR IMPLIED. USERS MUST TAKE FULL RESPONSIBILITY FOR THEIR APPLICATION OF ANY PRODUCTS.

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Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found atwww.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship

between Cisco and any other company.

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display

output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in

illustrative content is unintentional and coincidental.

Cisco ASR 5000 Session Control Manager Administration Guide

2013 Cisco Systems, Inc. All rights reserved.

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CONTENTS

About this Guide ................................................................................................ ixConventions Used .................................................................................................................................... xSupported Documents and Resources ....................................................................................................xi

Related Common Documentation ....................................................................................................... xiRelated Product Documentation ..................................................................................................... xiObtaining Documentation ............................................................................................................... xi

Contacting Customer Support ................................................................................................................. xiiSession Control Manager Overview ............................................................... 13

Product Description ................................................................................................................................ 14IMS Architecture ................................................................................................................................. 14

Proxy-CSCF ................................................................................................................................... 17Interrogating-CSCF ........................................................................................................................ 18Serving-CSCF ................................................................................................................................ 18Emergency-CSCF .......................................................................................................................... 20A-BG .............................................................................................................................................. 20

Technical Specifications ..................................................................................................................... 21Platform Requirements....................................................................................................................... 22Licenses ............................................................................................................................................. 22

Network Deployments and Interfaces .................................................................................................... 23SCM in a CDMA2000 Data Network Deployment .............................................................................. 23

Integrated CSCF / A-BG / HA ........................................................................................................ 23Logical Network Interfaces (Reference Points) ............................................................................. 23

SCM in a GSM/UMTS Data Network Deployment ............................................................................. 25CSCF / A-BG / GGSN Deployment ............................................................................................... 25Logical Network Interfaces (Reference Points) ............................................................................. 25

Voice over LTE (VoLTE) .................................................................................................................... 26CSCF Core / EPC Core Deployment ............................................................................................. 26

Features and Functionality - Base Software .......................................................................................... 28 AS Selection ....................................................................................................................................... 29ATCF/ATGW Support......................................................................................................................... 29Bulk Statistics Support ....................................................................................................................... 29Call Abort Handling ............................................................................................................................ 30Call Forking ........................................................................................................................................ 30Call Types Supported ......................................................................................................................... 31Congestion Control ............................................................................................................................. 31DSCP Marking .................................................................................................................................... 32Early IMS Security .............................................................................................................................. 32EATF Support ..................................................................................................................................... 32Emergency Call Support .................................................................................................................... 33Error Handling .................................................................................................................................... 33Future-proof Solution.......................................................................................................................... 33HSS Selection .................................................................................................................................... 33Intelligent Integration .......................................................................................................................... 33Interworking Function ......................................................................................................................... 34IPv6 Support ....................................................................................................................................... 34

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Management System Overview ......................................................................................................... 35MGCF Selection ................................................................................................................................. 36MSRP Support .................................................................................................................................... 37NPDB Support .................................................................................................................................... 37PCRF Policy Control ........................................................................................................................... 37Presence Enabled .............................................................................................................................. 37Redirection ......................................................................................................................................... 37Redundancy and Session Recovery .................................................................................................. 38Registration Event Package ............................................................................................................... 38Signaling Compression (SigComp) .................................................................................................... 38SIP Denial of Service (DoS) Attack Prevention .................................................................................. 38SIP Intelligence at the Core ................................................................................................................ 38SIP Large Message Support .............................................................................................................. 39SIP Routing Engine ............................................................................................................................ 39Shared Initial Filter Criteria (SiFC) ..................................................................................................... 39 Telephony Application Server (TAS) Basic Supported ...................................................................... 39Threshold Crossing Alerts (TCA) Support .......................................................................................... 41TPS (Transaction per Second) Based Overload Control Towards AS .............................................. 42Trust Domain ...................................................................................................................................... 42Features and Functionality - External Application Support .................................................................... 43Web Element Management System ................................................................................................... 43

Features and Functionality - Licensed Enhanced Feature Support ....................................................... 44 Interchassis Session Recovery .......................................................................................................... 44IPSec Support .................................................................................................................................... 45IPv4-IPv6 Interworking ....................................................................................................................... 45Lawful Intercept .................................................................................................................................. 47Session Recovery Support ................................................................................................................. 47SRTP Support in P-CSCF .................................................................................................................. 48TLS Support in P-CSCF ..................................................................................................................... 48

How the SCM Works .............................................................................................................................. 50Admission and Routing....................................................................................................................... 50

CSCF Access Control Lists ............................................................................................................ 50Translation Lists ............................................................................................................................. 50Route Lists ..................................................................................................................................... 50

Signaling Compression....................................................................................................................... 51Supported Standards .............................................................................................................................. 52

Release 9 3GPP References ............................................................................................................. 52Release 8 3GPP References ............................................................................................................. 523GPP2 References ............................................................................................................................. 54IETF References ................................................................................................................................ 55Other ................................................................................................................................................... 57

Configuration ..................................................................................................... 59Configuring the System to Perform as a Proxy-CSCF ........................................................................... 60

Initial Configuration ............................................................................................................................. 60Modifying the Local Context ........................................................................................................... 60Creating a P-CSCF VPN Context .................................................................................................. 61Creating the CSCF Service ............................................................................................................ 62

Proxy-CSCF Configuration ................................................................................................................. 62Setting the Systems Role as a Proxy-CSCF and Configuring Service Settings ........................... 62Identifying CSCF Peer Servers ...................................................................................................... 63Configuring Access Control and Route Lists ................................................................................. 63Setting the CSCF Policy and CSCF Session Template ................................................................. 63

P-CSCF Context Configuration .......................................................................................................... 64CSCF Logging Configuration ............................................................................................................. 64

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Save the Configuration ....................................................................................................................... 65Configuring the System to Perform as a Serving-CSCF ........................................................................ 66

Initial Configuration ............................................................................................................................. 66Modifying the Local Context........................................................................................................... 66Creating an S-CSCF VPN Context ................................................................................................ 67Creating the CSCF Service............................................................................................................ 68S-CSCF Context Configuration .......................................................................................................... 68

Serving-CSCF Configuration .............................................................................................................. 69Setting the Systems Role as a Serving-CSCF and Configuring Service Settings ........................ 69Identifying CSCF Peer Servers ...................................................................................................... 70Configuring Access Control, Translation, and Route Lists ............................................................ 70 Setting the CSCF Session Template ............................................................................................. 71Configuring DNS Connectivity ....................................................................................................... 71

Optional Interrogating-CSCF Configuration ....................................................................................... 71CDR Accounting Service Configuration ............................................................................................. 72CSCF Logging Configuration ............................................................................................................. 73Save the Configuration ....................................................................................................................... 73

Configuring the System to Perform as an Emergency-CSCF ................................................................ 74Setting the Systems Role as an Emergency-CSCF and Configuring Service Settings .................... 74CSCF Logging Configuration ............................................................................................................. 75Save the Configuration ....................................................................................................................... 75E-CSCF Call Flow .............................................................................................................................. 75

Configuring the System to Perform as an A-BG..................................................................................... 77 Access Context Configuration ............................................................................................................ 77Setting the Systems Role as an Access-Proxy and Configuring Service Settings ........................... 78CSCF Logging Configuration ............................................................................................................. 79Save the Configuration ....................................................................................................................... 79

Access Control Lists ........................................................................................ 81Understanding ACLs .............................................................................................................................. 82

Rule(s) ................................................................................................................................................ 82Actions ........................................................................................................................................... 82Criteria............................................................................................................................................ 83Rule Order .......................................................................................................................................... 85

Viewing ACLs ..................................................................................................................................... 85ATCF/ATGW Support ........................................................................................ 87

Feature Description ................................................................................................................................ 88Overview ............................................................................................................................................ 88Relationships to Other Features ........................................................................................................ 89

IPv6-IPv4 Interworking ................................................................................................................... 89Lawful Intercept (LI) ....................................................................................................................... 89Session Recovery .......................................................................................................................... 90

How it Works .......................................................................................................................................... 91Registration ........................................................................................................................................ 91

SRVCC Information Bound to the Registration Path ..................................................................... 92PS Session Establishment ................................................................................................................. 92PS-CS Transfer .................................................................................................................................. 92CS-PS Transfer .................................................................................................................................. 93Abnormal Procedures......................................................................................................................... 93Limitations .......................................................................................................................................... 93Flows .................................................................................................................................................. 93

Registration .................................................................................................................................... 94Session Establishment ................................................................................................................... 94Access Transfer (PS-CS) ............................................................................................................... 95

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IPv6IPv4 Mode in ATCF/ATGW ..................................................................................................... 97Standards Compliance ....................................................................................................................... 97

Configuring ATCF Functionality .............................................................................................................. 98Creating an ATCF Policy .................................................................................................................... 98Enabling ATCF Functionality in P-CSCF Service .............................................................................. 98 Verifying ATCF/ATGW Configuration ................................................................................................. 99Monitoring and Troubleshooting ATCF/ATGW ..................................................................................... 100ATCF/ATGW Show Command(s) and/or Outputs ........................................................................... 100

show cscf service ......................................................................................................................... 100clear cscf service .......................................................................................................................... 100show cscf service statistics name atcf ............................................................... 100show cscf service statistics name ...................................................................... 100show subscribers cscf-only full .................................................................................................... 101

ATCF/ATGW Bulk Statistics ............................................................................................................. 101EATF Support .................................................................................................. 103

Feature Description .............................................................................................................................. 104Overview ........................................................................................................................................... 104

How it Works ......................................................................................................................................... 105Limitations ........................................................................................................................................ 105Flows ................................................................................................................................................ 105

3GPP Signaling Flow for UE Initiating an Emergency Session in IMS ........................................ 1053GPP Signaling Flow for Emergency Session Transfer Using SRVCC Procedure..................... 106 IMS Emergency Session Transfer Using E-CSCF/EATF as per SCM ........................................ 107

Standards Compliance ..................................................................................................................... 109Configuring EATF ................................................................................................................................. 110

Configuring EATF ............................................................................................................................. 110Verifying EATF Configuration ........................................................................................................... 110

Monitoring and Troubleshooting EATF ................................................................................................. 111EATF Show Command(s) and/or Outputs........................................................................................ 111

show cscf service ......................................................................................................................... 111clear cscf service .......................................................................................................................... 111show cscf service statistics name eatf ............................................................... 111 EATF Bulk Statistics ......................................................................................................................... 111

IMS Rx Interface .............................................................................................. 113Feature Description .............................................................................................................................. 114

Overview ........................................................................................................................................... 114PCRF Policy Control .................................................................................................................... 114Diameter Protocol ........................................................................................................................ 115

How it Works ......................................................................................................................................... 116Flows ................................................................................................................................................ 116

Mobile Originated SIP Call (IMS UE) ........................................................................................... 117Mobile Terminated SIP Call (IMS UE) ......................................................................................... 118SIP Call Termination .................................................................................................................... 119ASR for an Existing Session (IMS and Non-IMS Clients) ............................................................ 119RAR for an Existing Session (IMS and Non-IMS Clients) ............................................................ 120Authorization Failure for Mobile Originated Call .......................................................................... 121Authorization Failure for Mobile Terminated Call @ 183 ............................................................. 122Call Hold ....................................................................................................................................... 123Call Waiting .................................................................................................................................. 124Subscription to Notification of Signaling Path Status ................................................................... 125 Disabling Early Media .................................................................................................................. 127

Standards Compliance ..................................................................................................................... 128Configuring an IMS Rx Interface .......................................................................................................... 129

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Creating and Configuring an IMS Rx Interface ................................................................................ 129 Configuring Rx Service Policy Rules ................................................................................................ 130Assigning Rx Service Policy to P-CSCF Service ............................................................................. 131Allowing Early Media on P-CSCF Service ....................................................................................... 131Configuring PCRF Policy Control Options ....................................................................................... 132Sample IMS Rx Interface Configuration ........................................................................................... 132

IP Security ........................................................................................................ 135Overview ............................................................................................................................................... 136IMS Security Network Scenarios .......................................................................................................... 137

Access Security ................................................................................................................................ 137Access and Network Domain Security ............................................................................................. 137

P-CSCF Security Support ..................................................................................................................... 141Security Association Setup for Subscriber Session ......................................................................... 142 Re-registration Handling .................................................................................................................. 144SA Lifetime Management ................................................................................................................. 147IMS Registration with USIM ............................................................................................................. 147

IPSec Configuration .............................................................................................................................. 148Creating and Configuring an IPSec Transform Set .......................................................................... 148Creating and Configuring a Crypto Template .................................................................................. 149Binding an IP Address to the Crypto Template ................................................................................ 149

Rf Interface Support ....................................................................................... 151Introduction ........................................................................................................................................... 152

Offline Charging Architecture ........................................................................................................... 152Charging Collection Function ....................................................................................................... 154Charging Trigger Function ........................................................................................................... 154Dynamic Routing Agent ............................................................................................................... 154

License Requirements...................................................................................................................... 154Supported Standards ....................................................................................................................... 154

Features and Terminology.................................................................................................................... 156Offline Charging Scenarios .............................................................................................................. 156

Basic Principles ............................................................................................................................ 156

Event Based Charging ................................................................................................................. 157Session Based Charging ............................................................................................................. 157

Diameter Base Protocol ................................................................................................................... 158Timer Expiry Behavior ...................................................................................................................... 159Rf Interface Failures/Error Conditions .............................................................................................. 159

DRA/CCF Connection Failure ...................................................................................................... 159No Reply from CCF ...................................................................................................................... 159Detection of Message Duplication ............................................................................................... 159CCF Detected Failure .................................................................................................................. 159

How it Works ........................................................................................................................................ 160Configuring Rf Interface Support .......................................................................................................... 162

Enabling Rf Interface in Active Charging Service ............................................................................ 162Configuring GGSN / P-GW Rf Interface Support ............................................................................. 163Configuring HSGW Rf Interface Support ......................................................................................... 170Configuring P-CSCF/S-CSCF Rf Interface Support ......................................................................... 180

Enabling Charging for SIP Methods ............................................................................................ 181Configuring S-GW Rf Interface Support ........................................................................................... 182Gathering Statistics .......................................................................................................................... 193

SIP DoS Attack Prevention ............................................................................ 197Feature Description .............................................................................................................................. 198

Overview .......................................................................................................................................... 198

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Flooding........................................................................................................................................ 198SIP Protocol Feature Exploitation ................................................................................................ 200

Standards Compliance ..................................................................................................................... 200Configuring SIP DoS Attack Prevention ............................................................................................... 201

Enabling SIP DoS Attack Prevention ............................................................................................... 201Configuring SIP DoS Attack Prevention ........................................................................................... 201

TLS Support ..................................................................................................... 203Overview ............................................................................................................................................... 204

TLS Session Renegotiation .............................................................................................................. 204TLS Session Setup ........................................................................................................................... 204TLS Session Tear Down................................................................................................................... 204P-CSCF Server Certificate ............................................................................................................... 204Use of TLS as Transport Between UE and P-CSCF ........................................................................ 205

TLS Setup Using 3GPP Approach ............................................................................................... 205TLS Setup Using RFC3261 Approach ......................................................................................... 206

Session Recovery ............................................................................................................................. 206PSC Migration .................................................................................................................................. 206Engineering Rules ............................................................................................................................ 206TLS Register Call Flow ..................................................................................................................... 207TLS 3GPP Approach Call Flow ........................................................................................................ 210

TLS Configuration ................................................................................................................................. 214Sample Configuration ....................................................................................................................... 214Creating the P-CSCF TLS Certificate ............................................................................................... 217Creating the Intermediate CAs in the Certificate Chain ................................................................... 217Creating the SSL Cipher Suite ......................................................................................................... 217Creating the SSL Template .............................................................................................................. 218Binding an SSL Template to a P-CSCF Service .............................................................................. 218

Sample Configuration Files ........................................................................... 219Proxy-CSCF Configuration ................................................................................................................... 220Serving-CSCF Configuration ................................................................................................................ 227A-BG Configuration ............................................................................................................................... 234

SCM Engineering Rules ................................................................................. 243

SCM Context and Service Rules .......................................................................................................... 244SCM Subscriber Rules ......................................................................................................................... 245AoR Regular Expression Rules ............................................................................................................ 246

Meta Characters ............................................................................................................................... 246AoR Regular Expression Patterns .................................................................................................... 246

Session Recovery Rules ....................................................................................................................... 248RFC 3261 Proxy ............................................................................................................................... 248

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OL-27224-07 ix

About this Guide

This preface describes the Cisco ASR 5000 Series Session Control Manager Administration Guide, how it is organized,

and its document conventions.

This preface includes the following sections:

Conventions Used

Supported Documents and Resources

Contacting Customer Support

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About this Guide

Conventions Used

Cisco ASR 5000 Session Control Manager Administration Guidex OL-27224-07

Conventions UsedThe following tables describe the conventions used throughout this documentation.

Icon Notice Type Description

Information Note Provides information about important features or instructions.

Caution Alerts you of potential damage to a program, device, or system.

Warning Alerts you of potential personal injury or fatality. May also alert you of potential electrical hazards.

Typeface Conventions Description

Text represented as a screendisplay

This typeface represents displays that appear on your terminal screen, for example:Login:

Text represented as commands This typeface represents commands that you enter, for example:show ip access-listThis document always gives the full form of a command in lowercase letters. Commands

are not case sensitive.

Text represented as a commandvariable

This typeface represents a variable that is part of a command, for example:show cardslot_numberslot_number is a variable representing the desired chassis slot number.

Text represented as menu or sub-menu names

This typeface represents menus and sub-menus that you access within a softwareapplication, for example:Click the Filemenu, then clickNew

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About this Guide



OL-27224-07 xi


Related Common Documentation

The most up-to-date information for this product is available in the product Release Notes provided with each product

release.

The following common documents are available:

Hardware Installation Guide(hardware dependent)

System Administration Guide(hardware dependent)

Cisco ASR 5000 Command Line Interface Referenc

Cisco ASR 5x00 AAA Interface Administration and Reference

Cisco ASR 5x00 GTPP Interface Administration and Reference

Cisco ASR 5x00 Product Overview

Cisco ASR 5x00 Release Change Reference

Cisco ASR 5x00 SNMP MIB Reference

Cisco ASR 5x00 Statistics and Counters Reference

Cisco ASR 5x00 Thresholding Configuration Guide

Mobility Unified Reporting and Analytics Installation and Administration Guide

Web Element Manager Installation and Administration Guide

Related Product Documentation

The following product documents are also available and work in conjunction with the SCM for VoLTE:

Cisco ASR 5x00 Gateway GPRS Support Node Administration Guide

Cisco ASR 5x00 HRPD Serving Gateway Administration Guide

Cisco ASR 5x00 Mobility Management Entity Administration Guide

Cisco ASR 5x00 Packet Data Network Gateway Administration Guide

Cisco ASR 5x00 Serving Gateway Administration Guide

Cisco ASR 5000 Serving GPRS Support Node Administration Guide

Cisco ASR 5x00 System Architecture Evolution Gateway Administration Guide

Obtaining Documentation

The most current Cisco documentation is available on the following website:

http://www.cisco.com/cisco/web/psa/default.html

Use the following path selections to access the SCM documentation:

Products > Wireless > Mobile Internet> Network Functions > Cisco ASR 5000 Session Control Manager

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About this Guide

Contacting Customer Support

Cisco ASR 5000 Session Control Manager Administration Guidexii OL-27224-07

Contacting Customer SupportUse the information in this section to contact customer support.

Refer to the support area of http://www.cisco.com for up-to-date product documentation or to submit a service request.

A valid username and password are required to access this site. Please contact your Cisco sales or service representative

for additional information.

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Chapter 1Session Control Manager Overview

This chapter contains general overview information about the Session Control Manager (SCM) including:

Product Description

Network Deployments and Interfaces

Features and Functionality - Base Software

Features and Functionality - External Application Support

Features and Functionality - Licensed Enhanced Feature Support

How the SCM Works

Supported Standards

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Session Control Manager Overview

Product Description

Cisco ASR 5000 Session Control Manager Administration Guide14 OL-27224-07

Product DescriptionThe Session Control Manager (SCM) delivers and controls a robust multimedia environment today, while preparing for

the networks of tomorrow. SCM provides an easy on-ramp to deploying Session Initiation Protocol (SIP)-based services

and a future-proof migration path to the IP Multimedia Subsystem/Multimedia Domain (IMS/MMD) architectures.

The SCM performs the following functions:

SIP routing

Translation and mobility

Admission control

Authentication

Registration

Emergency Registration

Packet network access based on pre-established policies and procedures

Localized policy selection and enforcement

Multimedia Call Detail Records (CDRs)

Per-subscriber service facilitation

SIP Application-level Gateway (ALG)

Media relay

Mitigate SIP Denial of Service (DoS)

Prevent registration hijacking

Prevent theft of service

The SCM consists of multiple IMS components that can be integrated into a single ASR 5000 platform or distributed asstandalone network elements:

IETF-compliant SIP Proxy/Registrar

3GPP/3GPP2-compliant Proxy Call/Session Control Function (P-CSCF)

3GPP/3GPP2-compliant Serving Call/Session Control Function (S-CSCF)

3GPP/3GPP2-compliant Interrogating Call/Session Control Function (I-CSCF)

3GPP/3GPP2 Breakout Gateway Control Function (BGCF)

3GPP/3GPP2-compliant Emergency Call/Session Control Function (E-CSCF)

3GPP/IETF-compliant Access Border Gateway (A-BG)

As standards-based network elements, SCM components can be integrated with each other or with third-party IMScomponents.

IMS Architecture

IP Multimedia Subsystem (IMS) specifies a standard architecture for providing combined IP services (voice, data,

multimedia) over the existing public switched domain. IMS is an integral part of the 3GPP, 3GPP2, ETSI, and TISPAN

network model standards that define circuit switched, packet switched, and IP multimedia domain environments. IMS

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Product Description


OL-27224-07 15

also supports multiple access methods such as CDMA2000, DOCSIS, EPS, Ethernet, Fiber, GPRS, WCDMA, WLAN,

XDSL, and wireless broadband access.

The call signaling protocol used in IMS is the Session Initiation Protocol (SIP). The primary component in the network

for resolving and forwarding SIP messages is the Call/Session Control Function (CSCF). The CSCF provides the

control and routing function for all IP sessions accessing the network. CSCFs are located in the control plane or layer ofthe Service Delivery Network as shown in the figure below.

When the SCM acts as an Access Border Gateway (A-BG), it uses the RFC3261/P-CSCF to provide a SIP/IMS control

plane access border, as well as a bearer access border control function. Therefore, the A-BG provides all session border

control functions for all SIP UEs attempting to access the mobile network from a network outside of the operator's

control and operations.

Figure 1. IMS Service Delivery Networks Components

Collectively, CSCFs are responsible for managing an IMS session, including generating Call Detail Records (CDRs).

Four functional behaviors are defined for the CSCF:

Proxy

Interrogating

Serving

Emergency

The following figure shows the general interaction between the CSCF components and the supporting servers.

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Product Description


Figure 2. IMS CSCF Components

In addition, the SCM may act as an Access Border Gateway (A-BG).

The following figure shows the general interaction between the A-BG and the supporting servers.

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Product Description


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Figure 3. Access Border Gateway

Proxy-CSCF

The primary point of entry into the IMS network is the Proxy-CSCF (P-CSCF). The P-CSCF is responsible for:

Providing message manipulation to allow for localized services (traffic/weather reports, news, directory services,

etc.)

Initiating the breakout of emergency service calls

Topology Hiding Inter-network Gateway (THIG)

Quality of Service (QoS) authorization

Number conversions for local dialing plans

Terminating IPSec tunnels

Transport Layer Security (TLS)

Interworking

Signaling Compression/Decompression (SIGCOMP)

Charging

The P-CSCF is the handsets first point of entry into the IMS and is also the outbound proxy for SIP. Once the P-CSCF

has completed all of the functions for which it is responsible, the call setup is handed off to the Interrogating-CSCF (I-

CSCF).

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Product Description


Interrogating-CSCF

The I-CSCF performs mostly as a load distribution device. The I-CSCF queries the Home Subscriber Server (HSS) to

identify the appropriate Serving-CSCF (S-CSCF) to which the call is sent. Since the HSS maintains user profile

information (much like the Home Location Register (HLR) in the Public Land Mobile Network (PLMN)), the I-CSCF

can identify the proper S-CSCF for the call. The I-CSCF may also query a AAA server to determine subscriber profile

information using DIAMETER.

Important: The I-CSCF is incorporated into the S-CSCF.

I-CSCF Interfaces

The following diagram shows the interfaces/reference points associated with the I-CSCF:

Serving-CSCFThe Serving-CSCF (S-CSCF) is the access point to services provided to the subscriber. Service examples include

session control services, such as call features.

Other services include:

VPN

Centralized speed dialing lists

Charging

The S-CSCF also interacts with the HSS for:

User authentication

Subscriber profile download and provisioning filter rules for services Network authentication key

Emergency registration

Location management

User data handling

A Breakout Gateway Control Function is integrated into the SCMs S-CSCF to support PSTN calls.

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Product Description


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Telephony Application Server (TAS) Basic Supported

The following describe the local basic call features implemented on the S-CSCF:

Abbreviated Dialing (AD)

Call Forward Busy Line (CFBL)

Call Forward No Answer (CFNA)

Call Forward Not Registered (CFNR)

Call Forward Unconditional (CFU)

Call Transfer

Call Waiting

Caller ID Display (CID)

Caller ID Display Blocked (CIDB)

Feature Code Activation/De-activation

Follow Me/Find Me

Locally Allowed Abbreviated Dialing

Outbound Call Restrictions/Dialing Permissions

Short Code Dialing

Integrated S/I-CSCF

The following Interrogating-CSCF features are supported for the integrated S/I-CSCF:

Assign an S-CSCF to a User Performing SIP Registration- On a UE registration, the I-CSCF carries out a

first step authorization and S-CSCF discovery. For this, the I-CSCF sends a Cx User-Authentication-Request

(UAR) to the HSS by transferring the Public and Private User Identities and the visited network identifier (all

extracted from the UE REGISTER message). The HSS answers with a Cx User-Authentication-Answer(UAA). The UAA includes the URI of the S-CSCF already allocated to the user. If there is no previously

allocated S-CSCF, the HSS returns a set of S-CSCF capabilities that the I-CSCF uses to select the S-CSCF.

E.164 Address Translation- Translates the E.164 address contained in all Request-URIs having the SIP URI

with user=phone parameter format into the Tel: URI format before performing the HSS Location Query. In the

event the user does not exist, and if configured by operator policy, the I-CSCF may invoke the portion of the

transit functionality that translates the E.164 address contained in the Request-URI of the Tel: URI format to a

routable SIP URI.

Obtain the S-CSCF Address from the HSS- When the I-CSCF receives a SIP request from another network, it

has to route the request to the called party. For this it obtains the S-CSCF address associated with the called

party from the HSS by querying with a Cx Location-Information-Request (LIR) message. The Public-Identity

AVP in the LIR is the Request-URI of the SIP request. The Location-Information-Answer (LIA) message

contains the S-CSCF address in the Server-Name AVP. The request is then routed to the S-CSCF.

Route a SIP Request or Forward Response from Another Network- When the I-CSCF receives a request

from another network, it obtains the address of the S-CSCF from the HSS using the procedure detailed above

and routes the request to the S-CSCF. Responses are also routed to the S-CSCF.

Perform Transit Routing Functions- The I-CSCF may need to perform transit routing if, based on the HSS

query, the destination of the session is not within the IMS. The IMS Transit Functions perform an analysis of

the destination address and determine where to route the session. The session may be routed directly to an

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Product Description


MGCF, BGCF, or to another IMS entity in the same network, to another IMS network, or to a CS domain or

PSTN.

Generate CDRs- The I-CSCF generates CDRs for its interactions. Upon completing a Cx query, the I-CSCF

sends an Accounting Request with the Accounting-Record-Type set to EVENT. The CDF acknowledges the

data received and creates an I-CSCF CDR.

Emergency-CSCF

The Emergency-CSCF (E-CSCF) is a network element in IMS which is responsible for routing an emergency call to a

Public Safety Answering Point (PSAP).

To identify the next hop PSAP, E-CSCF interacts with the Location Retrieval Function (LRF). LRF provides the

necessary routing information so that E-CSCF can route the request to the appropriate PSAP.

E-CSCF Interfaces

The following diagram shows the interfaces/reference points associated with the E-CSCF:

A-BG

The A-BG is responsible for:

Border Control for both Signaling and Bearer

CALEA Support

SIP and media taps

Call Admission and Access Control

Access Control based on IP, URL, SIP Identity, and Session Limits

Intelligent Routing Least Cost, Congestion Based, Call Type, Domain Based

As a SIP ALG, supports signaling and media routing with overlapping address ranges

SIP Application-level Gateway (SIP-ALG)

SIP NAT Traversal

SIP NAT (IPv4 IPv6 translation)

Media Relay (Header Manipulation): RTP, MSRP

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Product Description


OL-27224-07 21

SIP Security

Prevent Theft of Service

Prevent CSCF bypass

Robust authentication procedures

SIP message checking

Prevent Registration Hijacking

Authenticate Re-Register (S-CSCF)

Early IMS Security: DoS attack prevention, impersonating a server

UA authentication (prevent server impersonation)

AKA authentication mechanism (further protection)

Prevent Message Tampering (IPSec)

Prevent Early Session Tear Down

Early IMS Security prevents a different user releasing existing session

Mitigate SIP Denial of Service (DoS)

P-CSCF DoS Attack Prevention

Blocking of user/IP address

after repeated authentication and bad request failure in Register/INVITE

Dropping of Register

containing Contact header pointing to CSCF service ip:port

Limited number of contacts on which Forking is allowed

Dropping of Requests

coming from source address other than the Register request's source address Topology Hiding Inter-network Gateway (THIG)

Transport Layer Security (TLS)

Technical Specifications

The following table provides product specifications for the SCM.

Table 1. Session Control Manager Technical Specifications

DescriptionService Instances Dual-mode proxy: simultaneously supports IETF & 3GPP/3GPP2 Proxies

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Product Description


Description

SIP IETF SIP Proxy/Registrar

3GPP/3GPP2 Proxy Call Session Control Function (P-CSCF)

Stateful session and subscriber aware control

Signaling Compression/Decompression (SIGCOMP)

Auto discovery, subscriber privacy, network security, call fraud prevention, thwarting networkoverload conditions

SIP MessageHandling

Forking, error handling and discard, header stripping and insertion, multiple public user identities

Logical Interfaces IETF: SIP Proxy/Registrar

3GPP: Mw, Gm, Rx, Rf, Cx, Sh, Dx, MI

3GPP2: Mw, Gm, Tx, Rf, Cx, Sh, Dx, MI

Platform Requirements

The SCM service runs on a Cisco ASR 5x00 chassis running StarOS. The chassis can be configured with a variety of

components to meet specific network deployment requirements. For additional information, refer to the Installation

Guide for the chassis and/or contact your Cisco account representative.

LicensesThe SCM is a licensed Cisco product. Separate session and feature licenses may be required. Contact your Cisco

account representative for detailed information on specific licensing requirements. For information on installing and

verifying licenses, refer to theManaging License Keyssection of the Software Management Operationschapter in the

System Administration Guide.

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SCM in a CDMA2000 Data Network Deployment

Integrated CSCF / A-BG / HA

The SCM is designed to function within a CDMA2000 PDSN network. By combining the SCM with a carrier-class

Home Agent, a number of advantages emerge such as increased performance, distributed architecture, and high

availability. As shown in the figure below, the SCM supports a number of interfaces used to communicate with other

components in an IMS environment and supports the interface used to bridge the CDMA network.

Figure 4. CDMA2000 CSCF/A-BG/HA SCM Deployment Example

Logical Network Interfaces (Reference Points)

Interfaces, used to support IMS in a CDMA network, can be defined within two categories: SIP and DIAMETER. The

SCM incorporates standards-based interfaces for both SIP and DIAMETER network architectures.

SIP Interfaces

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The following table provides descriptions of SIP interfaces supported by the SCM in a CDMA2000 network

deployment.

Table 2. SIP Interfaces in a CDMA Network

Interface Description

Gm The reference point between the P-CSCF and the User Equipment (UE). The Gm interface provides SIP signalingbetween the PDSN and the P-CSCF.

MI The reference point between the E-CSCF and Location Retrieval Function (LRF).The MI interface is used for routing an emergency call to a Public Safety Answering Point (PSAP). The E-CSCFinteracts with the Location Retrieval Function (LRF) to identify the next hop PSAP.

Mw The reference point between the P/S-CSCF and other CSCFs.The Mw interface provides SIP signaling between twoCSCFs.

DIAMETER Interfaces

The following table provides descriptions of DIAMETER interfaces supported by the SCM in a CDMA2000 network

deployment.

Table 3. DIAMETER Interfaces in a CDMA Network


Cx The reference point between the S/I-CSCF and the Home Subscriber Server (HSS).The Cx interface is used to authenticate subscribers, provides server assignments, push user profile information fromthe HSS to the S-CSCF, and, when necessary, transmit a network initiated de-registration.

Dx The reference point between the S/I-CSCF and Subscriber Location Function (SLF).The Dx interface is used to proxy queries to a subscriber data server (such as an HSS) in which subscription data for auser can be found. The SLF receives a query for the subscriber data server, looks up the address of appropriatesubscriber data server, and proxies the query to the appropriate subscriber data server.

Rf The reference point between the P-CSCF and the Offline Charging System (OFCS).The Rf interface is used to transfer charging information that will not affect, in real-time, the service being rendered.For more information, refer to the 3GPP2 specification X.S0013-007-A v1.0.

Sh The reference point between the S-CSCF and Home Subscriber Server (HSS).The Sh interface is used for retrieval and update of call feature data parameters.

Tx The reference point between the P-CSCF/A-BG and the Charging Rule Function (CRF)/Policy Decision Point (PDP)(PCRF) used for Service Based Bearer Control (SBBC). It identifies any P-CSCF/A-BG restrictions to be applied to the

identified packet flows.

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SCM in a GSM/UMTS Data Network Deployment

CSCF / A-BG / GGSN Deployment

The SCM is designed to function within a UMTS GGSN network. As shown in following figure, the SCM supports a

number of interfaces used to communicate with other components in an IMS environment and supports the interface

used to bridge the GGSN network.

Figure 5. GSM/UMTS CSCF/A-BG/GGSN SCM Deployment Example

Logical Network Interfaces (Reference Points)

Interfaces, used to support IMS in a UMTS network, can be defined within two categories: SIP and DIAMETER. The

SCM incorporates standards-based interfaces for both SIP and DIAMETER network architectures.

SIP Interfaces

The following table provides descriptions of SIP interfaces supported by the SCM in a GSM/UMTS network

deployment.

Table 4. SIP Interfaces in a GSM/UMTS Network


Gm The reference point between the P-CSCF and the User Equipment (UE).The Gm interface provides SIP signaling between the GGSN and the P-CSCF.

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MI The reference point between the E-CSCF and Location Retrieval Function (LRF).The MI interface is used for routing an emergency call to a Public Safety Answering Point (PSAP). The E-CSCFinteracts with the Location Retrieval Function (LRF) to identify the next hop PSAP.

Mw The reference point between the P/S-CSCF and other CSCFs.The Mw interface provides SIP signaling between two CSCFs.

DIAMETER Interfaces

The following table provides descriptions of DIAMETER interfaces supported by the SCM in a GSM/UMTS network

deployment.

Table 5. DIAMETER Interfaces in a GSM/UMTS Network

Interface DescriptionCx The reference point between the S/I-CSCF and the Home Subscriber Server (HSS).

The Cx interface is used to authenticate subscribers, provides server assignments, push user profile information fromthe HSS to the S-CSCF, and, when necessary, transmit a network initiated de-registration.

Dx The reference point between the S/I-CSCF and Subscriber Location Function (SLF).The Dx interface is used to proxy queries to a subscriber data server (such as an HSS) in which subscription data for auser can be found. The SLF receives a query for the subscriber data server, looks up the address of appropriatesubscriber data server, and proxies the query to the appropriate subscriber data server.

Rf The reference point between the P-CSCF and the Offline Charging System (OFCS).The Rf interface is used to transfer charging information that will not affect, in real-time, the service being rendered.For more information, refer to the 3GPP2 specification X.S0013-007-A v1.0.

Rx The reference point between the P-CSCF/A-BG and the Charging Rule Function (CRF)/Policy Decision Point (PDP)(PCRF).The Rx interface (3GPP 29.211) is used to exchange Flow Based Charging (FBC) control information between thePCRF and the P-CSCF/A-BG. The CRF uses the information to make FBC decisions that are then exchanged with theTraffic Plane Function (TPF).This interface is used in a 3GPP2 Release 7 implementation.

Sh The reference point between the S-CSCF and Home Subscriber Server (HSS).The Sh interface is used for retrieval and update of call feature data parameters.

Voice over LTE (VoLTE)

CSCF Core / EPC Core Deployment

Mobile operators are migrating to the next generation 4G architecture based on Long Term Evolution (LTE) and the

Evolved Packet Core (EPC). LTE/EPC supports only IP-based services, and it does not provide a method for legacy CS

voice transport. The migration from circuit-based voice to packet voice and multimedia services is a key consideration

in the successful deployment of an LTE/EPC solution. Operators must consider how to migrate and deploy an

infrastructure that enables the introduction of a full suite of SIP-based services that provide subscribers with their

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existing voice and SMS services plus sets the framework for additional services, including video, Push to Talk over

Cellular (PoC), IPTV, presence, and instant messaging.

IMS has been chosen as the standard for providing circuit-based services over the all-IP LTE infrastructure. The long-

term strategy based on IMS has been under standardization in 3GPP using MMTel TAS in conjunction with SCC server

(TS 23.237) and the standard IMS core. In addition, the One Voice Initiative, a group of operators and carriers, hasdefined the preferred way to ensure the smooth introduction and delivery of voice and SMS services on LTE networks

worldwide. One Voice aims to ensure compatibility between networks and devices by creating a common profile, which

defines an optimal set of existing 3GPP functionalities for use by vendors and operators. The One Voice initiative has

accelerated the move to an IMS solution for LTE networks.

Cisco's ASR 5000 chassis supports two major elements for the evolution of voice and SMS from the circuit network to

the target network IMS. The ASR 5000 provides an LTE/EPC solution with high performance and integrated

intelligence. The Cisco MME, as part of the ASR 5000, supports Circuit Switch Fallback as a baseline capability. In

addition, the same ASR 5000 supports the full high performance IMS CSCF core (P/I/S/E-CSCF and BGCF)

functionality. This functionality can be provided as a standalone function or integrated into the EPC functions to provide

lower Total Cost of Ownership for the solution. For example, the P-GW and SCM can be integrated into a single

multimedia core platform. This reduces the cost of entry and the transition to VoLTE, thus lowering the OPEX, plus

reduces the number of network elements, network interfaces, and call set up latency.

Other features include:

Easy on-ramp, with interworking of RFC3261 SIP and IMS SIP

High availability, with intra/inter-chassis session recovery

Intelligent integration

IP mobility, with access-independent platform (mobile, WiFi, WiMAX, etc.)

Performance and scalability

Regulatory service support

Support for local number portability

Support for emergency call

Support for Lawful Intercept

SIP routing engine

Secure and controlled deployment

SIP routing, translation, and monitoring

Support for route failover and back up route selection

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Features and Functionality - Base SoftwareThe following is a list containing a variety of features found in the SCM and the benefits they provide.

This section describes the following features:

AS Selection

ATCF/ATGW Support

Bulk Statistics Support

Call Abort Handling

Call Forking

Call Types Supported

Congestion Control

DSCP Marking

Early IMS Security

EATF Support

Emergency Call Support

Error Handling

Future-proof Solution

HSS Selection

Intelligent Integration

Interworking Function

IPv6 Support

Management System Overview

MGCF Selection

MSRP Support

NPDB Support

PCRF Policy Control

Presence Enabled

Redirection

Redundancy and Session Recovery

Registration Event Package

Signaling Compression (SigComp)

SIP Denial of Service (DoS) Attack Prevention

SIP Intelligence at the Core

SIP Large Message Support

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SIP Routing Engine

Shared Initial Filter Criteria (SiFC)

Telephony Application Server (TAS) Basic Supported

Threshold Crossing Alerts (TCA) Support

TPS (Transaction per Second) Based Overload Control Towards AS

Trust Domain

AS Selection

The S-CSCF may select the Application Server (AS) peer server group based on subscriber prefix, ip-type, or capability

The selected AS group should have an active AS list, standby AS list, and default AS list.

In addition, the S-CSCF is able to skip third party registration to the AS by a configured time after initial registration.

After skipping the configured number of times, the third party register should be sent again to AS to reduce overload on

AS.

ATCF/ATGW Support

ATCF (Access Transfer Control Function)/ATGW (Access Transfer Gateway) functionality in P-CSCF service supports

Single Radio Voice Call Continuity (SRVCC) functionality. ATCF/ATGW provides proxy role and UA role, as per TS

24.237.

SRVCC refers to continuity between Internet Protocol (IP) Multimedia Subsystem (IMS)-over-Packet Switched (PS)

access and Circuit Switched (CS) calls that are anchored in IMS when the UE is capable of transmitting/receiving on

only one of those access networks at a given time.

SRVCC provides the ability to transition a voice call from the VoIP/IMS packet domain to the legacy circuit domain.

There are many standards which supports both GSM/UMTS and CDMA 1x circuit domains. For an operator with alegacy cellular network who wishes to deploy IMS/VoIP-based voice services in conjunction with the rollout of an LTE

network, SRVCC offers VoIP subscribers with coverage over a much larger area than would typically be available

during the rollout of a new network.

Important: For more information on ATCF/ATGW support, refer to theATCF/ATGW Supportchapter in thisguide.

Bulk Statistics Support

The system's support for bulk statistics allows operators to choose to view not only statistics that are of importance tothem, but also to configure the format in which it is presented. This simplifies the post-processing of statistical data

since it can be formatted to be parsed by external, back-end processors.

When used in conjunction with the Web Element Manager, the data can be parsed, archived, and graphed.

The system can be configured to collect bulk statistics (performance data) and send them to a collection server (called a

receiver). Bulk statistics are statistics that are collected in a group. The individual statistics are grouped by schema.

Following is a list of supported schemas for SCM:

Card: Provides card-level statistics

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Context: Provides context-level statistics

CSCF: Provides CSCF service statistics

CSCFINTF: Provides CSCF interface statistics

Diameter-acct: Provides Diameter Accounting statistics

Diameter-auth: Provides Diameter Authentication statistics

Map: Provides Map service statistics

Nat-realm: Provides NAT realm statistics

Port: Provides port-level statistics

System: Provides system-level statistics

The system supports the configuration of up to 4 sets (primary/secondary) of receivers. Each set can be configured with

to collect specific sets of statistics from the various schemas. Statistics can be pulled manually from the system or sent

at configured intervals. The bulk statistics are stored on the receiver(s) in files.

The format of the bulk statistic data files can be configured by the user. Users can specify the format of the file name,

file headers, and/or footers to include information such as the date, system host name, system uptime, the IP address ofthe system generating the statistics (available for only for headers and footers), and/or the time that the file was

generated.

When the Web Element Manager is used as the receiver, it is capable of further processing the statistics data through

XML parsing, archiving, and graphing.

The Bulk Statistics Server component of the Web Element Manager parses collected statistics and stores the information

in the PostgreSQL database. If XML file generation and transfer is required, this element generates the XML output and

can send it to a Northbound NMS or an alternate bulk statistics server for further processing.

Additionally, if archiving of the collected statistics is desired, the Bulk Statistics server writes the files to an alternative

directory on the server. A specific directory can be configured by the administrative user or the default directory can be

used. Regardless, the directory can be on a local file system or on an NFS-mounted file system on the Web Element

Manager server.

Important: For more information on bulk statistic configuration, refer to the Configuring and Maintaining BulkStatisticschapter in the System Administration Guide.

Call Abort Handling

Call abort handling provides resource cleanup in error scenarios and makes sure resources that are not being used can be

used for new calls. This feature is managed gracefully for a P-CSCF failure and CLI-initiated subscriber and session

clean up.

Call Forking

Call forking allows subscribers to receive calls wherever they are by enabling multi-location UE registration.

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Call Types Supported

In the IMS architecture, telephony features are normally provided by an external application server. Providing these

features with the S-CSCF:

Reduces the need for an additional SIP AS

Simplifies the network architecture

Improves latency for call setup and feature invocation

The following call types are supported:

Directory service, toll-free, long distance, international, and operator-assisted calls- are supported through

translation lists.

Emergency calls -are managed through the addition of an Emergency Call/Session Control Function (E-CSCF)

that routes emergency calls to a Public Safety Answering Point (PSAP).

Mobile-to-Mobile SIP calls- supports SIP-based VoIP calls between mobile data users.

Public Switched Telephone Network (PSTN) calls- can be routed through a 3GPP/2 compliant BGCF located

in the S-CSCF.

Congestion Control

The congestion control feature allows you to set policies and thresholds and specify how the system reacts when faced

with a heavy load condition.

Congestion control monitors the system for conditions that could potentially degrade performance when the system is

under heavy load. Typically, these conditions are temporary (for example, high CPU or memory utilization) and are

quickly resolved. However, continuous or large numbers of these conditions within a specific time interval may have an

impact the systems ability to service subscriber sessions. Congestion control helps identify such conditions and invokes

policies for addressing the situation.

Congestion control operation is based on configuring the following:

Congestion Condition Thresholds:Thresholds dictate the conditions for which congestion control is enabled

and establishes limits for defining the state of the system (congested or clear). These thresholds function in a

way similar to operation thresholds that are configured for the system as described in the Thresholding

Configuration Guide. The primary difference is that when congestion thresholds are reached, a service

congestion policy and an SNMP trap, starCongestion, are generated.

A threshold tolerance dictates the percentage under the configured threshold that must be reached in order for

the condition to be cleared. An SNMP trap, starCongestionClear, is then triggered.

Port Utilization Thresholds: If you set a port utilization threshold, when the average utilization of all

ports in the system reaches the specified threshold, congestion control is enabled.

Port-specific Thresholds: If you set port-specific thresholds, when any individual port-specific threshold is reached, congestion control is enabled system-wide.

Service Congestion Policies: Congestion policies are configurable for each service. These policies

dictate how services respond when the system detects that a congestion condition threshold has been

crossed.

CSCF performs congestion control based on the memory usage inside every sessmgr at two levels.

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Level 1: For every new call/event received, the system checks if sessmgr memory-usage is above a threshold value

(such as 95 percent). If it is, memory-congestion is triggered and new call messages are rejected with 500 SIP response.

Memory congestion is disabled when memory usage drops by a tolerance value (default is 10 percent).

Level 2: If the sessmgr usage reaches 100 percent, all newly received SIP messages are dropped at the socket layer in

that sessmgr except for the BYE message. The new SIP messages are not processed until the memory reaches thethreshold value (95 percent).

A trap is also generated whenever sessmgr is in congestion state.

Important: For more information on congestion control, refer to the Congestion Controlchapter in the SystemAdministration Guide.

DSCP Marking

Provides support for more granular configuration of DSCP marking.

For Interactive Traffic class, the P-CSCF/A-BG supports per-service configurable DSCP marking for Uplink andDownlink direction based on Allocation/Retention Priority in addition to the current priorities.

The following matrix may be used to determine the Diffserv markings used based on the configured traffic class and

Allocation/Retention Priority:

Table 6.Default DSCP Value Matrix

Allocation Priority 1 2 3

Traffic Handling Priority

1 ef ef ef

2 af21 af21 af21

3 af21 af21 af21

Early IMS Security

Early IMS security allows authenticating the UE without IMS protocols and clients. Based on the 3GPP TR 33.978

specification, the SCM supports security inter-operation with 2G and non-IPSec user devices.

EATF SupportSingle Radio Voice Call Continuity (SRVCC) refers to continuity between Internet Protocol (IP) Multimedia Subsystem

(IMS)-over-Packet Switched (PS) access and Circuit Switched (CS) calls that are anchored in IMS when the UE is

capable of transmitting/receiving on only one of those access networks at a given time.

SRVCC provides the ability to transition a voice call from the VoIP/IMS packet domain to the legacy circuit domain.

There are many standards which supports both GSM/UMTS and CDMA 1x circuit domains. For an operator with a

legacy cellular network who wishes to deploy IMS/VoIP-based voice services in conjunction with the rollout of an LT

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